1. Field of the Invention
The invention relates to flexible surgical instruments incorporating a hollow lumen coil. More particularly, the invention relates to a surgical instrument with a hollow lumen coil having areas of different preload tension to effect areas of different stiffness and flexibility in the coil, and to methods for imparting different preload tension to the coil.
2. State of the Art
Flexible surgical instruments, in particular endoscopic biopsy forceps and tissue scrapers, are used for taking tissue samples from the human body for analysis. These instruments typically have a long flexible hollow lumen coil containing one or more control wires coupled to a proximal actuating handle which moves the control wires relative to the coil to effect a tissue sampling operation at the distal end of the coil. In biopsy forceps devices, a pair of forceps jaws are mounted on a clevis at the distal end of the coil and coupled to the one or more control wires so that movement of the control wires causes the jaws to open and close to bite a tissue sample. In biopsy tissue scrapers, a brush or scraping tool is attached to the distal end of the coil and the control wire flexes the distal end of the coil to cause the scraping of a tissue sample.
The endoscopic biopsy procedure is accomplished through an endoscope which is inserted into a body and guided by manipulation to the biopsy site. The endoscope typically includes a long narrow flexible tube with an optical lens and a narrow lumen for receiving a biopsy forceps or tissue scraper. The practitioner guides the endoscope to the biopsy site while looking through the optical lens and inserts the biopsy forceps or tissue scraper through the lumen of the endoscope to the biopsy site. While viewing the biopsy site through the optical lens of the endoscope, the practitioner manipulates the actuating handle to effect a tissue sampling operation at the distal end of the instrument. In the case of biopsy forceps, the practitioner must align the open jaws with the tissue to be sampled so that upon closing the jaws, a portion of the tissue is trapped between the jaws. It is a known problem with biopsy forceps that as the jaws are closed the distal end of the flexible coil deflects because the force applied at the actuating handle to the control wires is transferred to the distal end of the flexible coil. The deflection of the distal end of the coil just as the jaws are about to close on a tissue to be sampled often displaces the jaws relative to the tissue to be sampled and results in a failure to acquire the sample or the acquisition of an undesired sample. Therefore, in the case of biopsy forceps, it is desirable to stiffen the distal portion of the coil to prevent it from deflecting when the jaws are being closed.
Co-assigned U.S. Pat. No. 5,228,451 to Bales et al. discloses a biopsy forceps device having a stiff distal portion. The distal portion of the flexible coil is made stiff by wrapping it with a stiffening sleeve which extends for several inches along the coil and covers a portion of the clevis. While the sleeve advantageously stiffens the distal portion of the coil, it also increases the outer diameter of the coil and provides an uneven surface. The increased diameter of the coil at the location of the sleeve is can hinder the travel of the coil through the narrow lumen of the endoscope. The uneven surface of the coil can also possibly cause undue wear or damage to the inner surface of the endoscope lumen.
Biopsy scraping tools, on the other hand, rely on the ability of the distal end of the coil to flex. Although the coil is generally flexible throughout its length, in a biopsy scraping tool, it is desirable to provide added flexibility at the distal end of the coil. U.S. Pat. No. 4,936,312 to Tsukagoshi shows a flexible body cavity inserting instrument which is a biopsy scraping tool. The tool has a long flexible coil attached at its proximal end to an actuation handle and one or more control wires which extend from the actuation handle through the coil to the distal end of the coil. The distal end of the control wire is coupled to a part of the distal end of the coil or the end effector so that pulling on the control wire causes the distal end of the coil to flex like a finger. A resilient member at the distal end of the coil returns the coil to a straightened position when tension on the control wire is released. A scraping end effector such as a brush or a cup with a sharp edge is fixedly attached to the distal end of the coil. To take a biopsy sample, the scraping end effector is positioned up against a tissue to be sampled and the actuating handle is manipulated to cause the distal end of the coil to flex. The flexing of the distal end of the coil causes the scraping end effector to move across the surface of the tissue to be sampled and to scrape off a sample. Tsukagoshi enhances the flexibility of the coil's distal end by providing the coil with a loosely wound distal end. At the distal end of the coil, the spirals forming the coil are spaced farther apart than the remainder of the coil which is closely wound with the spirals of the coil close together. The enhanced flexibility of the distal end allows it to bend up to 180 degrees which, in addition to enhancing the efficacy of the scraping end effector, also allows the tool to be bent to sample tissues which cannot be reached by an endoscope.
It is apparent, therefore, that in flexible surgical instruments having hollow lumen flexible coils, it is sometimes desirable to stiffen the distal portion of the coil and it is sometimes desirable to enhance the flexibility of the distal portion of the coil. Unfortunately, the known methods of altering the flexibility of the distal portion of the coil each have significant drawbacks. Moreover, the manufacturing procedures used to enhance the flexibility of the distal portion of the coil are so different from those used to stiffen the distal portion of the coil that the coils cannot be manufactured with the same machines. In addition, it is often desirable to stiffen the proximal portion of the coil to prevent buckling of the coil when the coil is inserted through an endoscope.